(function (doc, win) {
      var docEl = doc.documentElement,
          resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',
          recalc = function () {
              var clientWidth = docEl.clientWidth;
              if (!clientWidth) return;
              if(clientWidth>=750){
                  docEl.style.fontSize = '100px';
              }else{
                  docEl.style.fontSize = 100 * (clientWidth / 750) + 'px';
              }
          };
  
      if (!doc.addEventListener) return;
      win.addEventListener(resizeEvt, recalc, false);
      doc.addEventListener('DOMContentLoaded', recalc, false);
  })(document, window);